Michael Flynn, former national security adviser to President Donald Trump, has pleaded guilty to charges filed against him by special counsel Robert Mueller in the ongoing Russia investigation.

With legal bills mounting and a felony indictment for lying to the FBI on his record, Flynn's star has fallen rapidly since his days as a decorated lieutenant general and counterterrorism strategist. As part of his guilty plea he is now reportedly cooperating with the Mueller investigation, and seems poised to implicate those in the president's circle in the Russia case.

Here's how Flynn's roller coaster career led him to Friday's plea hearing:

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Flynn was born in 1958 in Rhode Island, and attended the University of Rhode Island where he began his military career by enrolling in the ROTC in 1981. He joined the US Army after graduating with a degree in management science.

Flynn's first deployment was to the island of Grenada, which the US invaded under former President Ronald Reagan to counter a leftist coup in the country. Flynn served as a platoon leader during the short engagement.

Flynn was promoted numerous times throughout his many years in the military, and in 2001 he was named director of intelligence for Joint Task Force 180 in Afghanistan. A year later he became the commander of the 111th Military Intelligence Brigade in the country.

Michael Flynn wearing his military honors. He was stationed in a variety of posts in Hawaii, Louisiana, and Arizona before serving in intelligence posts in Afghanistan.
Lauren Victoria Burke/AP Photo

Flynn was named the director of the Defense Intelligence Agency in 2012 by former President Barack Obama. But he was forced out in 2014, and his attempts at reform at the agency were deemed "disruptive."

Flynn at the National Security Alliance's Intelligence Community Summit on September 12, 2013 in Washington, DC. Flynn was named head of the Defense Intelligence Agency after stints gathering intelligence on Afghanistan and Iran.Win McNamee/Getty Images

Flynn claimed was fired from the DIA because he spoke out against "radical Islam," but he told The Washington Post at the time that the friction had more to do with the fact that he was seen as too hawkish.

After retiring from the DIA, Flynn formed his own private consulting firm called the Flynn Intel Group, which soon developed close ties to the Turkish government. Flynn was also criticized for attending a gala in 2015 that was held by pro-Putin channel Russia Today.

Former National Security Adviser Michael Flynn and Sebastian Gorka. Gorka is holding Flynn's book "Field of Fight," which he published in summer 2016. Flynn has come under fire for work he was doing on the Turkish government's behalf while serving as an unofficial advisor for the Trump campaign in 2016.
Facebook / Sebastian Gorka

Following Trump's surprise presidential win in November 2016, Trump named Flynn his national security adviser during the transition period. He had already served as an informal advisor since February, and he met Trump for the first time in August 2015.

Flynn's tenure with the Trump campaign was marked by several incendiary tweets. One stated that "fear of Muslims is RATIONAL."

A few weeks before Trump's inauguration in January 2017, Flynn met with former Russian ambassador Sergey Kislyak, who agreed to moderate Russia's response to then-President Barack Obama's sanctions against the country as a result of Flynn's advice. He pleaded guilty to lying about this exchange.

Flynn also came under fire for his lobbying in Turkey, and his short tenure as White House national security adviser was rocked by controversy. He eventually resigned in February after only 25 days in the position, largely due to revelations about his meeting with Kislyak.

Trump speaks by phone with Putin in the Oval Office at the White House in Washington. Flynn is seated on the far right.
Thomson Reuters

As allegations against Trump, Flynn, and others in the 2016 campaign mounted, the Russia investigation was launched. But Trump fired then-FBI Director James Comey, who initially headed up the probe, in May 2017 after reportedly telling him to stop investigating Flynn.

Flynn, James Comey, James Clapper and others testify before the before the Senate Intelligence Committee in January 2014. After Comey's firing, former FBI director Robert Mueller III was named special counsel for the investigation.Pablo Martinez Monsivais/AP

After Comey's departure, attention continued to coalesce around Flynn's connections to Russia and Turkey. In November, indications emerged that he was in fact cooperating with Mueller's investigation after his lawyers severed ties with Trump's legal team.

Among other allegations, Michael Flynn was accused of discussing potentially delivering a Muslim cleric living in the US to the Turkish government.
Kevin Hagen/Getty Images

These suspicions were confirmed by Flynn himself after he pleaded guilty to lying to the FBI about his meeting with Kislyak. "I recognize that the actions I acknowledged in court today were wrong, and, through my faith in God, I am working to set things right," he said.

Former national security advisor Michael Flynn walks to his plea hearing on December 1, 2017 before admitting he was cooperating with Mueller and regretting his dishonesty.Jonathan Ernst/Reuters